The teeth are anchored in alveolar bone which is a highly vascularized bony tissue specialized in supporting the teeth. The alveolar bone in turn is supported by intramembranous bone. Such bone is only found in the region of the skull. Bone is covered by a rich fibrous layer of tissue called the periosteum which acts as a reservoir for bone producing cells.
Alveolar bone forms a ridge or process which surrounds and supports the teeth. When a tooth is lost due to injury or disease, the section of alveolar bone which supported the tooth is rapidly resorped by the body. Much of the original mass and strength of the bone is lost through this natural remodeling process. Atrophy or loss of alveolar bone may also occur as the result of trauma to the bone, infection, radiation, congenital abnormalities or degenerative bone diseases. The severity of thinning or atrophy relates to the number of teeth lost and the time elapsed since the occurrence of the loss. The alveolar bone eventually becomes so thin and fragile that it can not reliably support dental prostheses or implants. A loss of chewing efficiency results which, in turn, gives rise to other problems such as uneven tooth wear, tooth migration, fractures, infection and facial deformity.
The general approach to the treatment of tooth loss is to attempt to restore function by fitting a prosthesis, dental implant, or through orthodontic intervention. These efforts become more difficult and less successful when bone loss has occurred. Unfortunately, when they fail, additional bone is lost, remodeling continues, and the potential for future correction is diminished.
Implants often fail because there is not enough bone mass available to support them. In younger patients, implants do not maintain the same height as neighboring teeth, which erupt as part of the natural growth and development process of the craniofacial complex. Over time, these implants submerge with respect to the adjacent teeth, reducing chewing efficiency and forming a trap for food debris and bacteria. This condition promotes infection of the bone surrounding the implant and leads to bone loosening and eventual failure of the implant. In the upper jaw, tooth loss can initiate an undesirable remodeling of the bony walls of the sinuses. As this bone thins out, and the sinus expands, it becomes difficult to fit a prosthesis or implant.
Edentulous patients suffer ongoing bone loss as the alveolar ridges are resorped. This leads to knife edge ridges which are ineffective in supporting prostheses such as dentures.
Moving teeth through atrophic alveolar ridges during orthodontic treatment leads to a number of problems. One in particular is the occurrence of root exposure as the teeth are moved through the atrophic bone. Periodontal disease and tooth loss can follow.
To overcome this, grafts of bone or biocompatible materials such as hydroxylapatite are used to increase the bone mass in areas of bony atrophy. Unfortunately, such procedures have high morbidity and a relatively low success rate. The results are unpredictable at best. Another problem is that after implantation, bone grafts must be shielded from loading until the graft takes. During this time, the graft undergoes remodeling, making it difficult to predict the final size and shape of the augmented alveolar ridge. The bone graft may also be rejected with subsequent failure of ridge augmentation.
Replacement of bone with hydroxylapatite may help regain some of the lost support in the area, but teeth cannot be moved through this bone substitute. Implants that are anchored in hydroxylapatite have a high failure rate due to mechanical breakdown at the hydroxylapatite-implant junction. Hydroxylapatite is also difficult to shape and is never as strong as natural bone. Some replacement of hydroxylapatite by new bone tissue does occur in the body but this material is never completely replaced by new bone.
Bone grafting and the use of hydroxylapatite is a traumatic and expensive procedure which requires a significant amount of time for healing to take place.
Defects also occur in the intramembranous bone. For instance, these may be caused during the extraction of teeth leading to oro-nasal fistulae. These are openings between the mouth and the sinuses. They are generally closed by placing grafts of gum tissue over the deficit. For large defects, the success of such grafts is limited. The treatment of such defects is best served by restoring the structure and shape of the area of lost bone.
Also, developmental defects occur in intramembranous bone, such as is seen in the clefts of the palate. In these anomalies, patients are born with defects of intramembranous bone in the roof of the mouth. Filling of these defects requires multiple surgeries over the individual's lifetime with bone and soft tissue grafts. Usually the results accomplished through such procedures only partially restore the shape, mass, and strength of the bone in the roof of the mouth.
Dental endosseous implants are subject to both axial and lateral stresses during mastication. An approach to stabilizing against lateral stresses uses implants which have the tooth embedded parts widened by either using the shape memory effect or the use of a wedge bolt post implantation. However, these approaches are not reliable and do not provide adequate lateral stabilization. Such implants also can not be used in areas were bone mass and strength are lacking.
The object of this invention is to provide a device and method for enhancing the shape and increasing the mechanical strength of alveolar and intramembranous bone. It functions by promoting the growth of new alveolar and intramembranous bone in a rapid and predictable manner where loss of this bone has occurred.